The present disclosure relates to an organic electroluminescence display device.
In an organic electroluminescence element (abbreviated to an organic EL element) forming an organic electroluminescence display device (abbreviated to an organic EL display device) which uses electroluminescence (hereinafter, abbreviated to EL) as an organic material, a stacked structure formed by stacking an organic hole transport layer, an organic light-emitting layer and the like is provided between a lower electrode and an upper electrode, on which attention is focused as a light-emitting element capable of emitting light at high luminance by low-voltage DC driving.
Since the above organic EL element has a response speed of 1 microsecond or less, duty driving by a passive matrix system is possible in the organic EL display device. However, when the duty ratio becomes higher with the increase of the number of pixels, it is necessary to supply large electric current instantaneously to the organic EL element in order to secure sufficient luminance, which tends to cause damage to the organic the organic EL element.
On the other hand, in an active matrix drive system, signal voltage is held by forming a storage capacitor as well as a thin-film transistor (hereinafter, abbreviated to TFT) at each sub-pixel. Therefore, it is possible to constantly supply drive current according to the signal voltage to the organic EL element during a desired period in one display frame. Accordingly, it is not necessary to supply instantaneously large current to the organic EL element such as in the passive matrix system, which reduces damage to the organic EL element. Note that one pixel usually includes three kinds of sub pixels which are a red light-emitting sub pixel emitting red color, a green light-emitting sub pixel emitting green color and a blue light-emitting sub pixel emitting blue color.
In the above organic EL display device of the active matrix drive system, as showing schematic partial cross-sectional view in FIG. 13 and showing schematic partial plan view in FIG. 14, a TFT is provided on a first substrate 11 so as to correspond to each sub pixel, and these TFTs are covered by an interlayer insulating layer 16 (a lower interlayer insulating layer 16A and an upper interlayer insulating layer 16B). A lower electrode 121 which is electrically connected to the TFT is provided on the upper layer interlayer insulating layer 16B by each sub pixel. An insulating layer 124 is further formed on the upper interlayer insulating layer 16B including the lower electrode 121, and an opening 126 in which the lower electrode is exposed at the bottom thereof is provided in the insulating layer 124. A stacked structure 123 is provided at a portion from a portion over the lower electrode 121 exposed at the bottom of the opening 126 to a portion 124′ of the insulating layer 124 surrounding the opening 126, which includes a light emitting layer made of an organic light-emitting material. An upper electrode 122 as a common electrode is formed on the insulating layer 124 including the stacked structure 123. A reference numeral 12 denotes a gate electrode included in the TFT, a reference numeral 13 denotes a gate insulating film included in the TFT, a reference numeral 14 denotes a source/drain region included in the TFT, a reference number 15 is a channel formation region included in the TFT, a reference numeral 17 denotes a wiring, a reference numeral 31 denotes a protection film, a reference numeral 32 denotes an adhesive layer, and a reference number 33 denotes a second substrate, which will be described in detail in Embodiment 1.
Since the stacked structures 123 are formed over the first substrate 11 on which the TFTs are formed through the interlayer insulating layer 16, in the case of an organic EL display device of a so-called bottom surface emitting type in which emitted light generated at the stacked structures 123 is taken out from the side of the first substrate, taken-out regions of the emitted light are narrowed by the TFTs. Therefore, it is desirable to apply an organic EL display device of a so-called top-surface emitting type in which emitted light is taken out from the second substrate 33 opposite to the first substrate 11.
In case that the organic EL display device of the top-surface emitting type is applied, the lower electrode 121 is usually made of a reflection material and the upper electrode 122 is made of a transparent conductive material or a semitransparent conductive material. However, the transparent material such as an oxide of indium and tin (ITO) or an oxide of indium and zinc (IZO), and the semitransparent material including a thin-film metal have a higher electric resistance value as compared with metals and the like. Therefore, a voltage gradient occurs in the upper electrode 122 as the common electrode, as a result, voltage tends to fall. When such voltage falling occurs, voltage to be applied to the stacked structure 123 forming each sub pixel will be uneven, which significantly reduces the display performance such that light emitting intensity at, for example, the central portion of a display area of the organic EL display device is reduced.
A means for addressing the above problems is well known in, for example, JP-A-2001-195008, or JP-A-2004-207217. In the technique disclosed in these patent documents, an auxiliary wiring 125 which is divided from the stacked structure 123 by the insulating layer 124 is provided, and the upper electrode 122 is formed from a portion over the stacked structure 123 to a portion over the auxiliary wiring 125 through the insulating layer 124. The auxiliary wiring 125 is made of a conductive material having a low electric resistance value such as metals.
The insulating layer 124 is often made of an organic material. After the insulating layer 124 having the opening 126 is formed over the insulating layer 16, plasma treatment using oxygen radical and the like is performed for cleaning up the surface of the lower electrode 121 exposed at the bottom of the opening 126. Organic matters and the like on the surface of the lower electrode 121 exposed at the bottom of the opening 126 are removed by performing the plasma treatment. However, as the result of performing the plasma treatment, the surface of the insulation layer 124 is also activated. For example, the insulating layer 124 includes a polyimide resin, a contact angle between the insulating layer 124 and water when the oxygen plasma treatment is not performed is approximately 78 degrees, however, the contact angle between the insulating layer 124 and water after the oxygen plasma treatment is performed is approximately 22 degrees.
To provide the auxiliary wiring 125 is useful because it prevents image quality from being lowered due to the voltage falling of the upper electrode 122. However, when the upper layer 124 is in the activated state as described above, particularly in case that the upper electrode is made of a semitransparent conductive material including a thin-film metal, a portion of the upper electrode 122 (non-overlapping portion 122′) on the insulating layer 124 connecting a portion of the upper electrode 122 on the stacked structure 123 to a portion of the upper electrode 122 on the auxiliary wiring 125 is degenerated when forming the upper electrode 122 after the stacked structure 123 is formed, which significantly lowers the conductivity. As a consequence, image quality deteriorates.
Thus, it is desirable to provide an organic EL display device having excellent display performance, including a configuration and a structure capable of reliably preventing the degeneration of the portion of the upper electrode connecting the portion of the upper electrode on the stacked structure to the portion of the upper electrode on the auxiliary wiring.